There aren't many cards in the "we get a buff while the field is Umi" category to be worth it, and for the ones that are there, Legendary Ocean is just better - it doesn't take a summon, it's not negated if there's an already-active field, it can't be killed in battle, and it has actual effects
Whether you pull it from a Mew Pack or craft it using Pack Points, Mew ex is an essential addition to any deck, adding powerful Psychic-type moves and strategic potential.
These cards also play well with Destructive Force (the slightly bigger version), and if youre playing Neheb, they can help clear the way for Commander damage
By embracing bounce spells, players not only expand their tactical toolkit but also enrich their EDH gaming adventures
Its all the better, as this spell will ensure you always have creatures in play to protect the enchanted Planeswalker